CANTON, Ohio — Cowboys starting left guard Nate Livings underwent arthroscopic surgery on his right knee Friday, a procedure that could sideline him for much of the preseason.

Coach Jason Garrett confirmed the surgery during his news conference at training camp in Oxnard, Calif. It was the second time in almost six months Livings has had the knee operated on.

He's expected to miss two to four weeks.

“Still, it's very early,” Garrett said. “Better to address those things right now and give those guys a chance to be ready for the start of the season.”

The Cowboys open their five-game preseason schedule Sunday against the Miami Dolphins in the Hall of Fame Game. The season opener vs. the New York Giants is Sept. 8 in Arlington.

Garrett declined to say whether quarterback Tony Romo would play against the Dolphins, but the injuries to the offensive line leave little doubt he and several other offensive starters will stay on the sideline Sunday.

“Typically, you don't play a lot in the first game of the four-game preseason schedule,” Garrett said. “You're going to see a lot of the younger guys play a lot in this ballgame.”

Dallas has been hit hard by injuries since camp started July 19. In addition to Livings, defensive end Anthony Spencer underwent arthroscopic knee surgery and also could be out for most of the preseason. Backup defensive end Tyrone Crawford is out for the season after tearing an Achilles tendon on the first day of camp.

Several other offensive linemen are injured, including three key backups: guard Kevin Kowalski (knee surgery), tackle Jermey Parnell (hamstring) and guard/center Ryan Cook (back). Guard Jeff Olson, one of the free agents Dallas signed Thursday to bolster depth, is out indefinitely after suffering a head and eye injury.

With Livings out, second-year pro Ronald Leary is expected to start against the Dolphins at left guard. The rest of the line likely will be filled by other youngsters and untested players.

In other injury news, tight end James Hanna returned to practice after missing most of camp with a hamstring injury.